The proteinaceous nuclear `matrix` or `scaffold` in the cell nucleus plays a role in determining chromatin structure. Electron micrographs show that nuclear DNA is attached to this scaffold at intervals to produce a series of loops (Zlatanova and Van Holde, J. Cell Sci. 103:889 (1992)). Matrix Attachment Regions (MARs; also referred to a scaffold attachment regions or SARs) are genomic DNA sequences which bind specifically to components of the nuclear matrix. See Boulikas, J. Cell. Biochem. 52:14 (1993). These sequences are thought to define independent chromatin domains through their attachment to the-nuclear matrix. Both transcription and replication are thought to occur at the nuclear matrix.
Transformation of a cell using a; transgene flanked by one or more MARs has been shown to increase expression of the transgene product, compared to transformation using a construct lacking MARs. See Allen et al., Plant Cell 8:899 (1996); Bonifer et al., EMBO J. 9:2843 (1990); McKnight et al., Proc. Natl. Acad. Sci. USA 89:6943 (1992); Phi-Van et al., Mol. Cell. Biol. 10:2303 (1990)). Flanking a GUS reporter gene with yeast MARs has been reported to result in higher and less variable transgene expression in plant cells. Allen et al. Plant Cell 5:603 (1993).